Revision Surgery in Otolaryngology
Head and Neck Surgery
Parotid-Benign Disease

John F. Carew, MD

Introduction

Parotidectomy for the primary treatment of tumors of the parotid gland, in general, is a satisfying surgical procedures. These tumors are usually benign, unifocal and freely mobile. With adequate surgical excision, including dissection and preservation of the facial nerve, the recurrence rate for these tumors is less than five percent.1-3 The cause of recurrence may be related to surgical technique, tumor biology or a combination of the two. Regardless of the cause of the recurrence, when they do reccur their surgical treatment can be tedious and technically challenging. In this chapter, the clinical characteristics of recurrent tumors of the parotid and their treatment will be discussed.
It should be noted that pleomorphic adenomas are by far the most common tumors to arise in the parotid gland.4 Not surprisingly, they are also the most common benign tumor to recur. For this reason, this chapter will present comment on recurrent pleomorphic adenomas of the parotid unless specified otherwise.

Factors Predisposing to Recurrence

Many factors have been linked to the recurrence of pleomorphic adenomas of the parotid gland. The first and most well-established factor is the extent of initial surgery. There is ample data to support the contention that the enucleation or limited local excision results in a high rate of recurrence. In series published in the past, where this surgical technique was used, high rates of recurrence were seen which approached 50 percent in some reports.5, 6 For this reason, it is now well accepted that adequate surgical excision with at least a small cuff of normal parotid tissue surrounding the tumor should be resected at time of primary treatment. It should be noted, however, that in many cases, at least a portion of the dissection is to close to the margin of the tumor during dissection of the facial nerve. Despite this, relatively low rates of recurrence are seen.
Occasionally, however, pleomorphic adenomas of the parotid gland may recur despite adequate primary surgical treatment. Several factors have been postulated to be related to this and include either tiny microscopic extensions of the tumor beyond the pseudocapsule of the tumor, multifocality of the tumor or rupture of the capsule of the tumor during primary surgical excision. While these factors seen intuitively obvious, retrospective reviews have failed to consistently reveal these as strong predictors of recurrence.7-9 These studies, however, are limited by several factors. First, most of these studies deal with a very small number of recurrent tumors since these tumors are uncommon and rarely recur. Additionally, they rely on operative reports for determining tumor capsule rupture. Unfortunately, operative reports do not always fully reflect the events that transpire. Surgeons may be hesitant to report capsule rupture for obvious medical legal reasons. Despite the limitations, several reports have failed to show a statistically significant increase in recurrence rate when the operative report specifically states that the tumor capsule was ruptured.7-9 In these manuscripts, the rate of recurrence when tumor capsule rupture is reported ranges from 0 - 8%. In all three studies, this is not significantly different from the recurrence rate when tumor capsule rupture is not reported. While these studies deal to show a relationship between tumor capsule rupture in recurrence, certainly there is anecdotal evidence that this may be a source of recurrence. This evidence stems from the fact that many times when pleomorphic adenomas of the parotid recur, there are multiple tumor nodule stunning the operative bed. Certainly, this pattern of recurrence is highly suggestive of tumors spillage as a possible mechanism for recurrence. Immunohistochemical studies have shown a high-level expression of integrin molecules on pleomorphic adenomas.10 These cell surface receptors are involved in cell-cell and cell-extracellular matrix interactions. Their presence may in part account for these cases where multiple tumors recur throughout operative bed.
While anecdotal evidence exists for tumor capsule rupture as an etiology for recurrence, more compelling evidence exists for microscopic extensions of tumor past the surgical margins. In one study, 57% of patients with microscopic extensions of tumor past the surgical margins had tumor recurrence.7 In another, however, positive surgical margins were not shown to increase the rate of recurrence.9 This factor, therefore, continues to remain controversial also. Again, however, the powerof these studies are limited by small sample sizes.
Finally, others have argued that this disease may be multifocal. History pathologic examples of tumor specimens rarely give evidence to support this. From the available data, it can be concluded that recurrent tumors may be the result of either inadequate initial surgery, rupture of the capsule of the tumor with contamination of the surgical bed or microscopic extensions of the tumor beyond its capsule. Regardless of the cause, when these tumors recur they present a surgical challenge.

Clinical Presentation/Preoperative evaluation

Pleomorphic adenomas of the parotid gland are relatively slow growing tumors. For this reason, recurrences often occur decades after the primary surgery. In evaluating a patient with recurrence, several important clinical factors should be considered. The nature of the primary surgical procedure and whether it was a formal parotidectomy or an enucleation. Treatment of patients with recurrent tumors that are the result of inadequate initial surgery tends to be more successful than the treatment of patients with recurrent tumors despite adequate initial surgery.11 Histologic characteristics of the primary tumor, with specific attention to the margins of the tumor and accuracy of the histologic diagnosis should be obtained. Whenever possible, the original slides should be obtained and reviewed to confirm the accurate histologic diagnosis. Another critical clinical factor is the disease free interval prior to recurrence and rate of growth of recurrent tumor. Additionally, the status of facial nerve function following the primary procedure is important to ascertain. If there was facial nerve weakness following the initial surgery, revision surgery will be more tedious and have a higher rate of facial nerve neuropraxia or permanent paralysis. Finally it is important to determine if there was a history radiation exposure or the use of therapeutic radiation in the past
In addition to the clinical history, several aspects of the physical exam are critical to the evaluation of the patient with a recurrent tumor of the parotid. The pattern of recurrence, unifocal vs. multifocal, is critical to surgical planning. Additionally, the relationship of the recurrent tumor to the overlying skin and scar tissue should be assessed. If the recurrence is immediately beneath the skin or the skin is tethered to the tumor, preparation should be made for sacrifice of the involved skin with appropriate reconstruction. The mobility of the tumor should also be assessed. The surgical incision should be inspected and kept in consideration when planning surgery for recurrent disease. In general, a modified blair incision is most commonly used and can be extended superiorly and inferior to give adequate exposure when necessary for resection of recurrent disease. Finally, the function of all branches of the facial nerve should be critically examined.
While evaluation of a patient with a primary parotid tumor may rely solely on clinical history and physical examination, in the recurrent setting it is important to obtain radiographic imaging as well as cytological evaluation. An MRI with attention to the parotid and parotid bed is highly sensitive for soft tissue disease. Oftentimes, radiographic imaging will show minute subcutaneous nodules not appreciated on physical exam. Additionally, it gives one a sense of the extent of previous surgery based on the amount of residual parotid gland remaining. Finally, it gives critical information with regards to the third dimension or depth of the tumor and its potential relationship to the facial nerve, parapharyngeal space and skull base.
It is often helpful to perform a fine needle aspiration biopsy to confirm the cytoological appearance of the cells within the tumor. Occasionally, recurrent tumors following excision of pleomorphic adenomas of the parotid will display a malignant histology. This is critical information to have for preoperative planning in that a more radical and aggressive oncologic resection would be performed for a high-grade malignancy as opposed to a recurrent pleomorphic adenoma. The limitations, however, of fine needle aspiration biopsy and cytological evaluation must be understood. A fine needle biopsy suggesting a recurrent pleomorphic adenoma does not guarantee that final histology will not show evidence of a malignant histology. The treatment of recurrent a pleomorphic adenoma which degenerates into a malignancy is beyond the scope of this chapter but requires a more aggressive surgical approach and a lower threshold for sacrifice of the facial nerve.

Surgical technique

The extent of surgery required to adequately reset a recurrent pleomorphic adenoma of the parotid gland depends in large part on the nature of the recurrence. Occasionally, one may see a unifocal recurrent just beneath the skin and sufficiently distant from the facial nerve that can be excised through a simple local excision. These cases, however, are relatively rare and this technique should be reserved for a very select cohort of patients. For unifocal reccurrences, the surgical technique is similar to that for primary parotid tumors although less parotid tissue will be encountered and the dissection of the facial nerve will be tedious. Surgical excision of the unifocal recurrence begins with entering the surgical bed using the previously made incision. Care must be taking in making this incision since the recurrence can often be just beneath the scan. Additionally, the facial nerve may be relatively superficial because the superficial lobe of the parotid is no longer separated from the skin. In revision surgery, the skin flap raised tends to be thinner than in primary surgery because of the potential superficial location of the tumor and facial nerve. In males, the base of the hair follicles can be used as a guide to raising the flap in a relatively superficial plane. In females, one must rely on meticulous dissection with frequent checks of the flap thickness. Once the flap has been raised the facial nerve should be identified. The initial attempt to identify the facial nerve can be made using the standard landmarks of the posterior belly of the digastric, tragal pointer and mastoid tip. If this region is heavily scarred, however, distal branches of the facial nerve can be identified and trace retrograde. As with any nerve dissection, it is critical to meticulously dissect directly on the nerve Oftentimes extensive fibrosis and strands of fibrous tissue will cover the nerve and can be confused for minuscule branches coming off the nerve. The meticulous dissection and the use of a nerve simulator may aid in distinguishing between strands of fibrous tissue and facial nerve branches. With careful and meticulous dissection, however, the vast majority of unique focal recurrent pleomorphic adenomas of the parotid can be resected with preservation of the facial nerve. It is exceedingly rare to have too resect the facial nerve to get adequate tumor resection. If a recurrent tumor, however, completing encases a single branch, this can be sacrifice and grafted. The functional anesthetic defect from this is reasonably acceptable. If, however, the main trunk of the facial nerve is encased with benign recurrent tumor, every effort should be made to preserve the nerve because of the significant aesthetic morbidity of sacrificing the main trunk even if it is reconstructed.
In multifocal and more advanced disease, more aggressive surgical approaches and more tedious dissection often required. If multiple subcutaneous nodules are seen beneath a scar, the scar tissue should be excised. Again, if a modified Blair incision had been used for the primary case, it is again used for the excision of the recurrence. As noted above, the skin flaps are raised in a superficial plane to protect the facial nerve and the recurrent tumor. When there is evidence of recurrence in surgical scar, oftentimes these tumors can be seen in the relatively superficial superficial subcutaneous tissue. Every effort should be made to appreciate these preoperatively and take adequate precautions to ensure adequate resection while maintaining the skin flap intact. Again, once the skin flaps have been raised the facial nerve should be identified. An initial attempt should be made at the usual landmarks of the tragal pointer and posterior belly of the digastric. Again, however, if heavy scarring is encountered here peripheral branches can be traced from distally to proximally. While it is rarely necessary to perform a mastoidectomy to identify the proximal facial nerve this maneuver can be considered in recurrent cases when there is massive recurrence, extensive multifocal tumors or extremely dense scar tissue. Once the facial nerve has been identified, meticulous dissection should be carried out along its branches. As previously described, a facial nerve simulator can be used to distinguish between twigs of fibrous tissue coming off the nerve versus true branches. Using the aforementioned methods, in general, most recurrent tumors, even when multifocal, can be safely resected with preserving the facial nerve.11
While the facial nerve integrity can be maintained in the vast majority of these cases, the rate of temporary nerve dysfunction following surgery for recurrent tumors is much higher than in primary cases. Because of this, one should carefully counsel the patient preoperatively that they may have temporary weakness of the face but that this usually will resolve with time. Additionally, technologies are now available which allow monitoring of the facial nerve which can help to identify its identification and minimize traumatic injury. While in the primary setting, facial nerve identification and atraumatic dissection is relatively straightforward, in the recurrent setting it can be very tedious. Certainly, routine use a facial nerve monitoring for primary parotid tumors is not necessary and has not been shown to improve outcome with regards to facial nerve function.12 In the setting of recurrent parotid tumors, however, it may serve as a useful adjunct to meticulous anatomic dissection. Some authors have reported it to be very useful for this purpose.13 As always, technology can never replace surgical experience, judgment and meticulous dissection.
The vast majority of primary parotid tumors as well as recurrences occur in the superficial lobe of the parotid. Occasionally, however, recurrent tumors may arise in the deep lobe. Again, proper clinical examination and radiographic imaging is critical to preoperative planning. Similar issues as described above apply to the treatment of recurrent parotid tumors in the deep lobe. In addition, further surgical exposure may be required for the resection of recurrent deep lobe parotid tumors. While the vast majority of primary deep lobe parotid tumors can be resected through a transcervical route, a small fraction of recurrent deep lobe parotid tumors may required a mandibulotomy to get adequate access for tumor resection. One should be prepared in the setting of a recurrent deep lobe parotid tumor to perform a mandibulotomy to ensure complete tumor removal. A mandibulotomy, however, it is still only required in a minority of cases even in the recurrent setting.
Adjuvant treatment in the form of postoperative radiation therapy should be considered in cases of multifocal recurrence, second or third reccurrences or if the surgeon is at all concerned with the adequacy of tumor resection.11, 14, 15 While gross tumor should never be left behind, there is a level of surgical satisfaction appreciated following tumor resection that should be taken into account when deciding if adjuvant radiation therapy is indicated. Certainly, there is a reasonable amount of data suggesting that in patients at high risk for further recurrence, postoperative radiation therapy decreases the rate of recurrence.11, 14, 15
Results
As mentioned earlier, parotid tumors are fairly slow growing and their recurrence can occur decades after initial treatment. For this reason, local control rate after treatment of recurrent pleomorphic adenomas is difficult to estimate and highly dependent on length of follow-up. Recent reports indicate that local control varies from 37% to 94 % (Table I).11, 14, 16-21 As would be expected, the studies with longer follow-up usually have higher rates of recurrence. The median time to failure in the treatment of recurrent pleomorphic adenomas was similar to the time to recurrence noted after initial surgery: 6.0 to 9.9 years.19, 20 In one report, none of the patients followed for less than ten years had recurrence, whereas 43% of patients followed more than ten years recurred.20
Several factors have been related to local control rates in the treatment of recurrent pleomorphic adenomas of the parotid. As expected, multifocal recurrences treated with surgery alone in one series had a much higher local failure rate (43%) compared to patients treated for unifocal disease (15% ).14 In another series, the extent of surgery for the primary tumor prior to the recurrence was related to local control rates for the treatment of the recurrence. Patients who recurred after an initial formal parotidectomy had a much higher local failure rate (37%) relative to patients who were treated for a recurrence after a limited excision (0% p < 0.01).11 The location of the recurrence deep to the facial nerve was also associated with a trend toward poorer local control. Patients with recurrences deep to the nerve had control rates of 67% at 7 years compared with 89% at 7 years for those with recurrence that was lateral to the nerve.11 This is not surprising given the difficulty in resecting deep lobe tumors in a previously operated parotid bed.
The last factor that appeared to improve local control was the use of post-operative radiation therapy (PORT) in select cases. In one series, the use of adjuvant postoperative radiation therapy improved local control rates in the cohort of patients with multi-nodular recurrences from 57 % to 96% (p < .01).14 In another series, the ten-year local control rate was 100% in patients who received adjuvant postoperative radiation therapy compared to 71% in those patients who did not receive postoperative radiation therapy.11 This difference, however, was not statistically significant (p<0.28) but may be related to the sample size and power of this study. In another study, the tumor was controlled in 18 of 20 patients (90%) whose recurrence was treated with excision and postoperative radiation therapy with follow-up ranging from 10 to 26 years.15 The recurrence in these patients, however, followed a limited initial operation, a setting in which a more favorable prognosis can be anticipated. Although, this issue is unlikely to be resolved by a randomized clinical trial, the evidence suggests that adjuvant PORT after surgery may benefit selected patients with ominous clinical and pathological presentations.

Conclusion

As with many recurrent disease processes, the adequate initial treatment of a tumor can avoid recurrence which often results in a much more tedious and technically challenging operation. Once a parotid tumor does recur, however, its successful treatment is facilitated by adequate preoperative clinical, radiographic and cytologic evaluation. Adequate surgical resection can often be achieve through an unhurried and meticulous dissection with careful localization and preservation of the facial nerve. Finally, despite adequate surgical excision, a cohort of patients exist who are at significant risk for recurrence. Specifically these are patients with recurrence after an initial adequate formal parotidectomy and those with extensive multi-nodular disease. These patients may benefit from adjuvant radiation therapy.

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